In the construction of thin film electroluminescent display devices, there is a requirement for a hermetic seal to protect the device against contamination. Water vapor is in particular damaging to the thin films that are deposited in constructing the display device. Any water or humidity penetration of the hermetic seal causes rapid degradation in display performance. Even relatively slow water penetration substantially shortens the useful life of the display. This hermetic seal is typically provided between the glass substrate upon which the thin films are deposited, and a cover sheet usually in the form of a protective glass plate.
At the present time, there are two types of hermetic seals that are predominantly used; one an epoxy seal and the other a glass frit seal. The epoxy hermetic seal particularly has problems under excess humidity conditions. Present epoxy seals are effective under high humidity conditions for only up to periods of seven hundred hours of operation. The glass frit seal does not suffer from degradation under high humidity conditions, but it does break down at higher temperatures.